The help lines need to be redrawn one step after a justification
(whether it has been undone or not, to replace "Unjustify" with
"Uncut" again for ^U), and after switching buffers (to update a
possibly changed tag for ^T).

This fixes https://savannah.gnu.org/bugs/?51455.

The precalculation of the multiline regexes no longer looks at the
keyboard every second, and the backup code makes use of futimens()
nowadays.

Well, it will compile even without that include.  :|
I don't know why, since it does use va_list.

get_chunk_row() replaces the formula "column / editwincols".

get_chunk_leftedge() replaces "(column / editwincols) * editwincols".

get_last_chunk_row() replaces "strlenpt() / editwincols".

get_last_chunk_leftedge() replaces "(strlenpt() / editwincols) * editwincols".

This prepares us for any changes in those formulas, and for more such
functions later.

This partially adresses https://savannah.gnu.org/bugs/?50998.

It's useless, because the position doesn't get restored, and it
cannot be restored because the name is different every time.

This extra question was included upon Chris' request, but I find it
confusing and angering.

When spotlighting the string to be replaced, placewewant isn't valid,
so tell place_the_cursor() to ignore its value to avoid the cursor
getting mistakenly placed at the beginning of the next row.

This fixes https://savannah.gnu.org/bugs/?50997

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

Also, allow Ctrl+Left/Right with --enable-tiny --enable-browser.

Also remove a superfluous check for 'do_replace' -- it never gets
bound in the Search/Replace menus.

When configured with --enable-tiny --enable-multibuffer,
/do/ include the new-buffer toggle in the Read-File menu.

Add missing spaces, remove excess spaces, and
replace groups of indentation spaces with tabs.

Things have morphed over time and display_buffer() no longer actually
displays the buffer -- it just displays the title bar, precalculates
the multiline color info, and schedules a refresh of the edit window.

This avoids https://savannah.gnu.org/bugs/?49912 while at the same time
avoiding to draw the edit window twice in a row -- the first drawing
would use a wrong margin, which results in a visible and irritating
shift left or right of the content upon the second drawing.

This fixes https://savannah.gnu.org/bugs/?50877.

When nano has multiple files open, closing a help buffer should
not switch to the next buffer in the ring but to the preceding one,
because it was from there that the help screen was invoked.

Allow the user to search in a help text with ^W and M-W.

Achieve this by not writing the help text directly to the screen
but first writing it to a temporary file and then opening this file
in a new buffer, and treating it specially: the normal file-reading
feedback is suppressed, the titlebar shows the headline of the text,
the cursor is hidden, and the menu is limited to just the up and down
movements and searching.

This fulfills https://savannah.gnu.org/bugs/?28994

.
Signed-off-by: Rishabh Dave <rishabhddave@gmail.com>

Call something a buffer when it refers to a linked list of linestructs,
and call something a linestruct when it is a struct that describes a
single line.

Trim a superfluous assert too.

File formats, appending and prepending, and backups are not available
when --enable-tiny is used, so prevent all relevant pieces of code from
getting compiled.  And correct two misspelled ENABLE_TINY to NANO_TINY.

Because nothing gets reset to zero or to some initial value.

The interval 2013-2017 for the Free Software Foundation is valid
because in those years there were releases with changes by either
Chris or David, and the GNU maintainers guide advises to mention
a new year in all files of a package, not just in the ones that
actually changed, and be done with it for the rest of the year.

Verify at startup that the number is not too small.

(We still leak the backupname in that case, but I can't be bothered
with that now.)

Also elide a variable, trim some comments, and rewrap some lines.

Use futimens() instead of utime() to change the timestamps on a backup
file.  Otherwise, a non-privileged user could create an arbitrary symlink
with the name of the backup file and in this way fool a privileged user
to call utime() on the attacker-chosen file.

Import the relevant gnulib module to make sure futimens() is available.

The "./" is a shorthand for "current working directory".
It is better to specify it, because it differs from what
Pico does: reading always from the user's home directory
no matter where the editor was started.

Only use the "from" thing when an operating directory is in effect,
because /only/ then the indicated directory can be something other
than "./".

Also, make it so that there is no space before the colon.

We want to be able to scroll the line at edittop partially off the
screen.  For this to be possible, the new variable firstcolumn stores
the starting column of the viewport -- the starting column in the line
that edittop points to.

Since firstcolumn is used by go_back_chunks() and go_forward_chunks(),
it can't be completely #ifdefed out when NANO_TINY is set, but outside
of softwrap mode it should always be zero.

Currently firstcolumn is initialized to zero, reset to zero when
toggling softwrap mode off, and reset to zero when switching buffers
while softwrap mode is off.  It's otherwise unused, but its uses are
forthcoming.

Since all lines can be partially scrolled off the screen now
(except for the top line of the edit window, which is forthcoming),
ensure_line_is_visible() is no longer needed.

Use less_than_a_screenful() again, just as in do_uncut_text().

Most of these variables are freed moments later -- reallocating
them is thus a waste of time.

Windows doesn't have *nix style account databases.

With read_file() revamped, it now uses partition_filestruct() indirectly
via ingraft_buffer(), so we can't use partition_filestruct() to replace
marked text in the alternate spell checker anymore without segfaulting.

Add the new function replace_marked_buffer() to accomplish this instead.
Based on replace_buffer(), it uses extract_buffer() to throw away the
marked un-spell-checked text, and then uses read_file() to insert the
spell-checked text at the position where the mark was.

Accordingly, remove unneeded partitioning and related stuff from
do_alt_speller().  Besides pasting the file into the buffer at
current[current_x], ingraft_buffer() also deals with renumbering,
updating totsize, and handling a magicline, so do_alt_speller()
doesn't need to do those anymore.

With read_file() revamped to handle inserting a file at the current
position, partitioning the buffer is no longer needed.